1. Field of the Invention
This invention relates to a level shifter circuit which converts a low-level input signal into a high-level output signal.
2. Description of the Related Art
With the recent progress of semiconductor technology, the transistor threshold voltage has been getting lower in the control driving circuit of a display unit, which enables the driving voltage of the controller IC to be made lower than before. In addition, a lower power consumption of applications has been strongly desired. For these reasons, the output signal of the controller IC tends to decrease in amplitude. Moreover, to reduce unnecessary radiation (EMI) noise, a lower-amplitude transfer of the interface signal has been strongly desired.
Therefore, it is desirable that a driving circuit equivalent to a driving IC should be composed of transistors in the substrate to enable the input signal supplied to the driving IC to directly operate the driving circuit in the substrate. However, because of the restrictions on use in the substrate, it may be necessary to amplify the amplitude of the input signal. In this case, a level shifter circuit for amplifying the amplitude of the signal is used (refer to Jpn. Pat. Appln. KOKAI Publication No. 2007-178451).
However, when a peripheral circuit is formed on the same glass substrate using the same process as forming a pixel transistor as in a liquid-crystal display unit using thin-film transistors or an electroluminescent display unit, the transistor threshold value is more difficult to control than in a single-crystal silicon semiconductor and a fluctuation in the threshold voltage due to variations in the processes is particularly large. For these reasons, receiving the low-amplitude signal output from the controller IC, the level shifter circuit formed on the glass substrate sometimes failed to operate properly.